1. Field of the Invention
This invention relates to a process for reducing the stiffness of a nonwoven fabric. More particularly, the invention concerns such a process which subjects a stitchbonded nonwoven fabric to a stretching and relaxing treatment that not only makes the stitchbonded fabric less stiff, but also greatly increases its specific volume.
2. Description of the Prior Art
Stitchbonded fabrics and methods for producing them are known, as for example from K. W. Bahlo, "New Fabrics without Weaving" Papers of the American Association for Textile Technology, Inc. pp. 51-54 (November 1965). Such fabrics are made by multi-needle stitching of various fibrous substrates with elastic or non-elastic yarns, as disclosed, for example, by the present inventor in U.S. Pat. Nos. 4,704,321, 4,737,394 and 4,773,328. In the finishing operations, such as heat setting, drying or chemical finishing, the fabric may be heated and cooled while being held in a stretched condition, usually on a tenter frame. However, such operations usually result in undesirable stiffening of the fabric. Even without such treatments, known stitchbonded fabrics having unit weights of less than about 200 grams per square meter, generally are quite stiff and dense.
Supple fabrics of high bulk are particularly desired for certain apparel fabrics, insulating fabrics, powder puffs, dust cloths, cosmetics wipes, and the like. Accordingly, a purpose of this invention is to provide a process for decreasing the stiffness and density of a stitchbonded fabric.
Various methods have been suggested in the art for decreasing the stiffness of a nonwoven fabric by working the fabric. Such processes involving passage of a nonwoven fabric between peg rolls or button-breaker rolls, or through crepers, or the like, have been disclosed, for example, by Dempsey, U.S. Pat. No. 3,811,979 and Dempsey et al, U.S. Pat. No. 3,427,376.
Methods for stretching fabrics also are known. Such methods include: (a) long span, longitudinal stretching between two pairs of nip rolls operating at different speeds; (b) long span, transverse stretching on a tenter frame; (c) transverse microstretching between a pair of rolls, each roll having circumferentially extending and axially spaced grooves and lands which intermesh with the corresponding grooves and lands on the other roll, as disclosed by Lachenauer, U.S. Pat. No. 3,624,874; and (d) longitudinally and transversely microstretching in sequence, first between intermeshing axially grooved rolls and then between circumferentially grooved rolls, as disclosed by Schwarz, U.S. Pat. Nos. 4,223,059 and 4,438,167.